This invention relates generally to nuclear reactors and more particularly, to assemblies and methods for coupling core spray line assemblies within such reactors.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. Typically, the core spray piping is coupled to a thermal sleeve which is welded to a RPV nozzle, or safe end.
Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC.
Reactor internal piping, such as thermal sleeves and core spray lines, occasionally requires replacement as a result of SCC. Replacing the core spray piping often requires removing the core spray line from the RPV safe end. Because the spray line is welded to the safe end, removing the spray line from the safe end often damages, or breaks, the safe end. To replace the safe end, the reactor must be drained to an elevation below that of the safe end. The safe end is then cut off and a replacement is welded to the RPV. Thereafter, the replacement core spray line is welded to the replacement safe end. Replacing a safe end is time consuming and tedious.
It would be desirable to provide an assembly which facilitates replacing core spray lines without removing the reactor pressure vessel safe end. It also would be desirable to provide such an assembly which is easily removed and installed without the necessity of welding.